Recovery of Magnesium Hydroxide from Natural Saline Waters of the Bukhara Region by Sodium Hydroxide Precipitation
Baxshilloyev Nozim *
Department of Chemical Technology, Bukhara State Technical University, Bukhara, Uzbekistan.
Umirov Farkhod
Department of Chemical Technology, Navoi State University of Mining and Technologies, Navoiy, Uzbekistan.
Kucharov Baxrom
Institute of General and Inorganic Chemistry of the Academy of Sciences of the Republic of Uzbekistan, Tashken, Uzbekistan.
Maxmudov Rafiq
Department of Chemical Technology, Bukhara State Technical University, Bukhara, Uzbekistan.
*Author to whom correspondence should be addressed.
Abstract
Aim: This study evaluates natural saline waters from the Bukhara region as magnesium-bearing raw materials and to establish a rational sodium hydroxide precipitation regime for recovering magnesium as a magnesium hydroxide-rich product.
Study Design: A comparative laboratory study was conducted using natural saline waters collected from the Quyimozor and Olot areas. The effects of NaOH dosage and terminal pH on magnesium precipitation were evaluated, and the resulting solid product was characterized by XRD, FTIR and SEM–EDS analyses.
Place and Duration of Study: The study was conducted at Bukhara State Technical University, Bukhara, Uzbekistan, from January 2023 to May 2026.
Methodology: Magnesium was precipitated at 25 ± 2 °C using a 10 wt.% NaOH solution. The NaOH dosage was varied from 95 to 110% of the stoichiometric requirement. After reagent addition, the suspensions were mixed for 10–12 min and aged for 120–140 min. The precipitates were separated by filtration, washed with distilled water, and dried at 100–110 °C to constant mass. Magnesium precipitation was calculated from the magnesium mass balance between the initial saline water and the final filtrate. Each experimental condition was tested independently three times.
Results: The Quyimozor and Olot saline waters contained 2.58 and 2.10 wt.% Mg²⁺, respectively. Increasing the NaOH dosage from 95 to 105% increased magnesium precipitation from 75.0 to 99.2% for Quyimozor water and from 74.1 to 98.8% for Olot water. Increasing the dosage to 110% resulted in only a marginal improvement. Magnesium precipitation increased from 35.0% at pH 9.0 to 97.0% at pH 10.5 and 99.0% at pH 11.0. XRD analysis revealed characteristic reflections at 2θ values of 18.86°, 38.18°, 51.06°, 58.92° and 62.32°, confirming brucite-type Mg(OH)₂ as the principal crystalline phase of the recovered precipitate. FTIR analysis revealed a sharp structural hydroxyl band at 3695.05 cm⁻¹ and Mg–O lattice absorptions near 409–406 cm⁻¹. SEM images showed fine agglomerated particles, while EDS analysis of the selected area indicated 48.4 wt.% Mg and 51.6 wt.% O.
Conclusion: A NaOH dosage of 100–105% of the stoichiometric requirement and a terminal pH of 10.5–11.0 provided high magnesium recovery while limiting unnecessary alkali consumption. The combined FTIR and SEM–EDS results were consistent with the formation of a magnesium hydroxide-rich precipitate. XRD analysis confirmed brucite-type Mg(OH)₂ as the principal crystalline phase, while the FTIR and SEM–EDS results provided complementary structural, morphological and elemental evidence.
Keywords: Natural saline water, brine valorization, magnesium hydroxide, sodium hydroxide, precipitation, FTIR, SEM–EDS, XRD